I've always used a stick for flight sim, (currently a cheap Thrustmaster stick and throttle) but one of the things I find most difficult is trimming the aircraft. In a real aircraft trimming is 100x easier than in a sim as you pitch the aircraft, feel the pressure on the yoke, spin the trim wheel and instantly feel the pressure fall away until it's prefectly trimmed, in a couple of seconds. In a sim, I hold the pitch I want, press the trim button but have to guess where to stop. 

Does a yoke exist that replicates this pressure, or are they all on a fixed spring? Maybe I am being stupid and they all do this! 

Not really. A force feedback yoke might make this possible (no experience with them myself) but these often require lots of tweaking to get the feeling right, and that has to be done for each aircraft.
I found this document Trim functionality Brunner Yoke that may give you an indication what's involved.

Trimming is a good example where the real thing might actually be less difficult to do then in a simulator.

 

There are only a few high-end  yoke/stick with FFB that could provide such feeling.

But, IRL, big airliners which using the whole stabilizer to trim, behaive more like the fixed spring one (actually, it just is) as I know, 707,727, 777 and 787 is just dead spring on elevator for normal envelope. while 737 (and might also 747-767, I can't sure) have some centering mechanism to mimic GA, it only make a few degree of change thus still feel much like a dead spring.

If you feel hard on trim, it's more likly be the plastic mechanism in those cheap stick/yoke got uneven friction. so the force on your hand is not dynamicly proportional to the input as displacement.